Worsen

глагол а) ухудшаться Например: The weather has again changed and worsened. — Погода снова изменилась к худшему. б) ухудшать

Большой англо-русский словарь

Worsen

verb (worsened; worsening) transitive verb to make worse intransitive verb to become worse Example: the weather began to worsen

Merriam-Webster's Collegiate Dictionary